1. Field of the Invention
This invention relates to running bore-lining tubulars, and in particular to running tubulars into wellbores drilled, for example, to access sub-surface hydrocarbon-bearing earth formations.
2. Related Art
In the oil and gas exploration and production industry, wellbores are drilled from the Earth's surface to access sub-surface hydrocarbon-bearing formations. These bores are typically completed by being lined with metal tubulars, which are generally known as casing and together form a tubular string. The tubular string may be suspended or hung from the Earth's surface and the annulus between the exterior of the casing and the surrounding interior wall of the bore wall is typically filled and sealed with cement (“cased hole completion”). In some wellbore configurations, the drilled hole is left open at the reservoir section such that other tubulars, generally known as liners, can be suspended or hung from the lower end of a string of casing and pass through the portion of the wellbore that intersects the hydrocarbon-producing formations. As with casing, in a liner completion, the annulus between the liner and the wellbore wall may be sealed with cement, and the liner and cement subsequently perforated to provide a fluid flow path between the liner bore and the surrounding Earth formations. In other cases, a tubular string may comprise expandable tubulars which are run into a bore through existing casing and then radially, plastically expanded to a larger diameter below the existing casing to produce a lined bore of substantially constant diameter, known as “mono-bore”. Other tubular strings may comprise sand screens which are in effect tubular filters and which may be placed across formations which would otherwise produce large volumes of sand or other solid particulate material with the oil or gas. Such sand screens may also be radially plastically expandable.
A more recent innovation of a tubular string may comprise sections of tubulars welded together at surface to form one continuous string, substantially without threaded connectors.
In a typical conventional tubular string, large numbers of casing sections or “joints” are joined together end to end by typically threaded connectors to form the “string”, and the string is lowered (“run”) into the wellbore without rotation. The leading end of the casing string is run “barefoot” in many wells or provided with a profiled nose or “shoe”. Centralisers may be affixed to the exterior of the casing at selected intervals along the string to centralise the casing in the wellbore to facilitate cementing. However, running casing strings into wellbores is often difficult, and it is not unusual for a casing string not to reach the desired depth on the first run. In such event, the string must be withdrawn and the wellbore re-drilled or otherwise cleaned to remove the obstructions that may have prevented the casing from reaching the desired depth in the wellbore on the first run. Obstructions encountered by a tubular string may include beds of drill cuttings lying on the low side of an inclined bore, ledges, swelling formations, partial or complete borehole collapses, or other borehole discontinuities.
With a view to overcoming these difficulties there have been a number of proposals to provide casing shoes or wash down shoes with hydraulic jets and with cutting blades, and then to rotate the casing string as it is lowered into the bore. These various apparatus and methods have been effective in some instances, however conventional casing and casing connectors are not generally well suited to withstand applied torques, and there are also challenges in providing drive arrangements on drilling or workover rigs capable of handling larger diameter casing. There are also many forms of tubulars which are even less well suited to transferring torque, such as sand screens or slotted expandable tubulars. Furthermore some types of downhole strings by the nature of their design and construction absolutely require first time installation, such as expandable and welded downhole strings.
In a separate and related aspect of the process of drilling sub-surface wellbores from the Earth's surface, and specifically when wellbores are to be drilled under the seabed, a tubular known as a conductor pipe is initially run into the seabed from a platform, jack-up rig, semi-submersible or the like having the purpose of supporting the casing run into the subsequently drilled wellbore. Typically, the conductor is run through a slot in the platform or rig until refusal takes place (meaning until the conductor stops sinking into the seabed under its self weight). Typically refusal takes place at a depth above the required depth to which the conductor should be placed and as a result a pile driver is generally used to drive the conductor to its required depth or until refusal. This pile driving operation can take several days of rig time and thus constitutes an economic cost for the operation.
It is among the objectives of embodiments of the present invention to provide a means of overcoming obstructions encountered by a tubular string while being run into the wellbore which does not rely on the torque capacity of the tubular string, providing rotational drive arrangements on rigs and that allows tubular strings to be run to the desired depth in a timely and economic manner.
It is among the objectives of other embodiments of the present invention to provide a means of placing a conductor at the desired depth in a more timely and economic fashion than is possible using conventional methods.